A vehicle, such as an automobile, is generally equipped with a seatbelt device for restraining an occupant in a seat that includes a seat portion on which the occupant is seated and a backrest portion located to the rear of the occupant. Such a seatbelt device includes webbing used to restrain an occupant in a seat, a retractor for retracting the webbing, a guide anchor (webbing-threading member) mounted on a vehicle body for guiding the webbing, a belt anchor for fixing the webbing to the vehicle body, a buckle disposed on a side surface of the seat, and a tongue through which the webbing passes. An occupant is restrained by fitting the tongue into the buckle. In this seatbelt device, one end of the webbing is fixed to the belt anchor and another end of the webbing is thread through the guide anchor and joined to the refractor. Thus, at the time of withdrawing or retracting the webbing, the webbing is always in contact with and slides over the guide anchor.
At the time when a large load acting toward the front side of the vehicle is applied to an occupant, such as when a vehicle crashes or decelerates suddenly, the above guide anchor may cause a phenomenon in which the webbing is deviated toward the front side of the vehicle (what is called being jammed). As disclosed in PTL 1 to PTL 3, for example, some devices have been proposed as measures to prevent such a phenomenon. In each of the devices, a metal guide piece having certain grooves or recesses and projections is placed on a portion over which the webbing slides.
Here, a webbing-threading member described in PTL 1 has a recessed-and-projecting region that is only formed on a vehicle body side or on or around a top portion of a guide piece. A webbing-threading member described in PTL 2 is obtained by grinding recesses and projections formed on a surface of a guide piece to thus smooth the recesses and projections and reduce the frictional resistance. A webbing-threading member described in PTL 3 is obtained by forming, on a vehicle front side of a guide piece, grooves that extend in a direction in which the webbing extends when worn and that are curved toward the rear side of the vehicle.